The whole blood IFN-γ assays was approved by The Centers for Disease Control as an alternative screening strategy to TST in immunocompetent individuals [11], but its clinical utility as a single test for detection LTBI in immunocompromised patients is controversial.Furthermore, its utility in patients with psoriasis and psoriatic arthritis has not been yet established One hundred patients with psoriasis and psoriatic arthritis and 50 healthy control will participate in this study.